1. Field of the Invention
The present invention relates to an ELID centerless grinding apparatus for grinding an extra-fine component or an elongated component in the centerless manner.
2. Description of the Prior Art
As the optical communications or ultraprecision devices are developed, the needs for ultraprecision small-diameter cylindrical components used in ferrule or micro machine parts is increased, and the highly efficient and ultraprecise production technique is demanded. As such ultraprecision small-diameter cylindrical components, there are, for example, a fiber guide for an optical fiber connector, a needle of a needle bearing, a head of a dot printer and others. Application of the centerless grinding machine is suitable for processing an outside diameter of such a component having an extremely fine diameter (for example, not less than several mm) or that having high aspect ratio.
FIG. 1 is a block diagram showing an ELID centerless grinding apparatus reported by the inventor of the present invention (xe2x80x9cDevelopment and Practical Application of the ELID Processing Machine and System No. 4xe2x80x9d, Tool Engineers, October 1998).
As shown in the drawing, an elongated workpiece 1 is mounted on a blade 2 having a slant surface on an upper surface thereof and brought into contact with an outer peripheral surface of a regulating wheel 3 to rotate around a shaft center of the workpiece 1. On the other hand, an ELID electrode 5 and a discharge electrode 6 are provided in close vicinity to the outer peripheral surface of a conductive grinding wheel 4 such as a bronze-iron composite bond and the like, and a voltage for discharge or a voltage for electrolysis can be applied between these electrodes and the grinding wheel 4 by an ELID power supply 7.
With such a structure, precision truing of the outer peripheral surface of the grinding wheel can be carried out by discharge truing which can cause discharge between the discharge electrode 6 and grinding wheel 4 so that the very accurate grinding wheel surface having the straightness of 4 xcexcm/W50 mm and the roundness of 2 xcexcm/xcfx86150 mm can be obtained.
Further, a conductive electrolytic fluid 8 is supplied between the ELID electrode 5 and the grinding wheel 4 while performing the initial dressing of the grinding wheel 4 therebetween. Subsequently, the electrolytic dressing of the grinding wheel 4 is carried out while conducting the electrolytic in-process dressing grinding (ELID grinding) for grinding the workpiece 1 is performed. Consequently, it is possible to obtain ceramics (zirconia ferrule) or nitrided SKD 61 (hardness of 1000 HV) having a diameter of 2.5 mm which has the surface roughness of not more than Rz 0.15 xcexcm and the straightness of not more than Rp 0.15 xcexcm.
However, the above-described ELID centerless grinding apparatus has such a problem as that the outer peripheral surface shape of the regulating wheel 3 changes due to the long use. For example, in the in-feed grinding for grinding without feeding the workpiece, a part which comes into contact with the workpiece is worn away due to abrasion and, as a result, an contact area with the workpiece changes, which disables the smooth rotation. Further, in the through-feed grinding for grinding while feeding the workpiece, the regulating wheel 3 is partially worn away, thereby similarly disabling the smooth rotation.
Moreover, even if the outer peripheral shape does not change, when the surface aspect of the regulating wheel 3 changes to vary the coefficient of friction, the workpiece can not be smoothly rotated, and there occurs such problems as that the workpiece is processed to be flat (sectional shape distorted from the perfect circle).
When these problems occur, the regulating wheel 3 is removed from the apparatus to correct the shape in the offline manner or an additionally provided working tool is used to correct the outer peripheral surface on the machine without removing the regulating-wheel 3 from the apparatus in the prior art.
However, since the re-sharpening changes the coefficient of friction with respect to the workpiece in either case, the stable grinding is difficult under the same conditions. Further, in case of re-sharpening in offline in particular, attachment/reattachment disables the precise centering.
The present invention is made to solve the above-described problems. That is, an object of the present invention is to provide an ELID centerless grinding apparatus which can keep the coefficient of friction of the outer peripheral surface shape of the regulating wheel 3 with respect to the workpiece substantially constant during the grinding process of the workpiece.
According to the present invention, there is provided an ELID centerless grinding apparatus comprising: a blade (2) for horizontally supporting a rotator workpiece (1) and having a slant surface inclined outwards and downwards; and a regulating wheel (10) driven to rotate around a horizontal shaft center, a conductive grinding wheel (4) being used to ELID-grind the outer surface of the workpiece, an outer peripheral portion of the regulating wheel (10) including a conductive elastic member (11) and abrasion resisting particles (12) held by the member (11), and further comprising: an electrolytic electrode (14) provided in close vicinity to the outer peripheral surface of the regulating wheel (10); and an electrolytic power supply (16) for applying a voltage for electrolysis between the electrolytic electrode and the regulating wheel (10), the conductive electrolytic fluid flowing between the electrolytic electrode and the regulating wheel (10), the conductive elastic member (11) being removed by the electrolytic dressing, the abrasion resisting particles (12) being projected to rotate around a shaft center of the workpiece in contact with the outer peripheral surface of the workpiece.
According to the structure of the present invention, when the electrolytic voltage is applied between the electrolytic electrode (14) and the regulating wheel (10) by the electrolytic power supply (16) to subject the conductive elastic member (11) of the regulating wheel (10) to the electrolytic dressing while supplying the conductive electrolytic fluid 8 between the electrolytic electrode (14) and the regulating wheel (10), the conductive elastic member (11) can be removed by the electrolytic dressing to keep the outer peripheral surface shape of the regulating wheel (10) substantially constant during the grinding process of the workpiece, and a quantity of projection of the abrasion resisting particles (12) can be adjusted to keep the coefficient of friction with respect to the workpiece substantially constant.
According to a preferred embodiment of the present invention, the conductive elastic member (11) is a mixture of a elastic member and conductive particles.
With this structure, desired conductivity can be imparted to the conductive elastic member (11) by the conductive particles and the elasticity can be given to the same by the elastic member.
Other objects and advantageous features of the present invention will be apparent from the following description in conjunction with the accompanying drawings.